The present invention relates to a locking device for a wire line core drilling system in accordance with the preamble to claim 1, a wire line core drilling system including a locking device in accordance with the preamble to claim 9, and a method of wire line core drilling in accordance with the preamble to claim 10.
When performing exploratory drilling to collect rock samples from depths of from several hundred to a couple of thousand meters, double core tubes are used having an inner and an outer tube. The sample is collected in the inner tube, which usually has a length of a few meters. When the inner tube is full this is usually detected by means of a manometer or the like that measures the flushing water pressure in the core tube. A retriever device suspended on a wire is lowered into the tube for retracting the inner tube with the sample, said retriever device comprising a gripping means in the form of a claw or xe2x80x9cspear headxe2x80x9d arranged to engage with a gripping means arranged on/in the upper end of the inner tube. When the wire is then tautened the inner tube is disengaged from the outer tube, and the inner tube with the sample can be hoisted up. Conversely, the claw and gripping means on the inner tube can be used to lower a new inner tube. Equipment of this type is generally known as a wire line system.
When a new inner tube is inserted it is important to be able to ascertain that the inner tube really has reached right down to the bottom and has assumed its correct position for drilling, before drilling is commenced. Ascertainment that the tube cannot no longer move, but is firmly held is generally taken as an indication that the inner tube has reached its correct position. According to known technology, therefore, the gripping means is often designed to be combined with some type of locking member that firmly locks the inner tube in relation to the outer tube when the inner tube has reached the correct position. This locking member usually consists of a hook-like device, preferably spring-loaded, a locking claw or latch that engages with recesses or shoulders arranged in the inside of the outer tube. Actual insertion of the inner tube is usually performed by the inner tube being xe2x80x9cpumpedxe2x80x9d along inside the drill string with the aid of water, and/or lowered with the aid of the force of gravity. In the case or horizontal, or substantially horizontal holes the tube must be pumped along. When the inner tube is firmly in place the water pressure will increase to such an extent that a valve arranged for flushing medium in the inner tube is released.
One problem with such known arrangements is that when the inner tube is inserted into the drill string, it sometimes catches before it has reached the correct position for drilling. With designs currently in use the increase in water pressure then occurring will release the flushing valve before the inner tube has reached its correct position and, in the worst case, drilling will be commenced. This primarily entails a disadvantage from the financial point of view since the drilling will be into thin air. The same thing may naturally occur when a tube that has been lowered by the force of gravity gets caught and drilling is commenced since it is assumed that the inner tube has reached the correct position for drilling. There is also a risk of the core at the bottom being destroyed.
When the inner tube is full and shall be retracted the locking means in the form of locking claws or latches retaining the inner tube in the outer tube must be disengaged from the outer tube. This is usually achieved by the retractor claw engaging with the gripping means connected to the locking device, the latches of which then being drawn in against the action of the spring force that is pressing them outwards to achieve locking against the outer tube. A certain reaction force is thus necessary in the system in order to overcome the spring force, which also increases the friction at the point where the latches hook into the outer tube. Currently the most usual known device for achieving this comprises a sleeve that contributes to compressing the latches from below so that they are released from the recesses, shoulders, or the like of the outer tube. Other devices used to achieve this are described, for instance, in U.S. Pat. No. 4,834,198 and Swedish patent No. 320 941. The latter particularly reveals the drawback that gripping means and locking member are only engaged at one point, which naturally rally easily leads to load imbalances and problems associated therewith. Due to the design of the known devices, as the placing of the springs and the various gripping and locking members, however, the problem sometimes arises that the locking member is not released from its engagement with the outer tube, remaining caught there and preventing the inner tube from being retracted with the core sample. This may result in extensive standstill costs, as well as other costs. In fact, the complete drill string must then be taken up and the wire must be cut in every joint of the drill string. This is extremely time-consuming and expensive.
The primary object of the present invention is to remedy the problems described above by means of a single device.
The object of the invention is achieved by means of a locking device as defined in the characterizing part of claim 1, a wire line core drilling system as described scribed in the characterizing part of claim 9, and a method as described in the characterizing part of claim 10.
In accordance with the present invention, thus, a locking device for an inner tube comprises locking members so designed that, when the inner tube has been inserted into the outer tube and has assumed the correct position inside the outer tube for drilling, in one and the same movement it simultaneously effects mechanical locking of the inner tube in relation to the outer tube and mechanical release of a gripping means of an accompanying device connected to the inner tube. The invention thus offers the advantages that the accompanying device is not released until the inner tube has assumed the correct position inside the outer tube for drilling. This is particularly advantageous if, for instance, the accompanying device comprises a valve for flushing medium, which is usual as described above. When the valve is released, this is achieved mechanically with the aid of the locking device in accordance with the invention. Thus, it is not released as a result of any pressure increase, and the risks entailed with previously known pressure-released arrangements, e.g. that the valve is released when the tube catches, are therefore eliminated. The locking device in accordance with the invention also has the advantage that it can be used together with an accompanying device consisting of an insertion device for inserting an inner tube into an outer tube in a dry drill hole. A corresponding method is defined in claim 10.
Preferably, the locking device in accordance with the invention also comprises gripping means which, when the inner tube is to be withdrawn from the outer tube with the aid of a retriever device comprising gripping means, and said gripping means of the retriever device come into contact with the gripping means of the locking device, in one and the same movement engage with the gripping means of the retriever device and simultaneously release the inner tube from its locked position in relation to the outer tube. The invention thus reveals the additional advantage that the locking device and catch are disengaged from each other at the same time as the inner tube is released from being locked in relation to the outer tube.
The present invention thus offers the important advantage of being able to fulfil both the functions described, and also of being able to be used both together with a flushing valve and in a dry drill hole. It constitutes a more reliable, simpler and more economic solution than has been available through known technology.
In accordance with a particularly preferred embodiment the locking device comprises at least two parts, each of which is journalled pivotably in the inner tube in radial direction about a shaft situated between rear protrusions and forward protrusions on respective parts. It is these protrusions that act as means for firmly locking the inner tube in relation to the outer tube, engage with gripping means on the retriever device and also firmly lock or release the accompanying device. These protrusions and other components of the invention will be described in the following detailed description with reference to the drawings.
The invention also relates to a wire line core drill system including such a locking device, as defined in claim 9.
Additional features and advantages are revealed in the dependent claims.
The invention will now be described in detail with reference to the accompanying drawings, illustrating a non-limiting embodiment of the invention by way of example, in which:
FIG. 1 shows a longitudinal section through a drill string provided with a locking device in accordance with the present invention, upon insertion of an inner tube,
FIG. 2 shows a longitudinal section through a drill string provided with a locking device in accordance with the present invention, where the inner tube has assumed its correct position for drilling, and the flushing valve has been released,
FIG. 3 shows a longitudinal section through a drill string provided with a locking device in accordance with the present invention, and illustrates how a retriever device is inserted into the locking device, and
FIG. 4 shows a longitudinal section through drill string provided with a locking device in accordance with the present invention, where the inner tube is inserted into a dry drill hole.